Do you notice that your reader also makes grammatical errors in her speech?
You are right.
Aherville no doubt existed before Zindel was born, and will continue to do so after his death. That there are observant Jews in Aherville is presented as a fact of life in Aherville. Would it make sense to say, "Everyone celebrated Shabbos every week..." if Shabbos was still being celebrated AFTER Zindel had a good meal; and would still be by the end of your story?
Present Tense is used for a fact which is 'universal', 'timeless', where a beginning and an end to the event/action is irrelevant.
Using the Past tense = no more, over, done. The only way this could be - the use of the Past Tense - is if you wrote, "...was celebrated every week, but the demands of modern life on people's time had dwindled this to a monthly event. Their fervour, however, remains strong: a case of the spirit is willing, but their social calendars are full."
"The Flying Scotsman departs Edinburgh for London at 9.37 p.m. every morning. It was a typically bleak day in Edinburgh when Zindel boarded the train, his heart far heavier then the suitcase he carried."
As for a reference/citation, I''m sure Thornton Wilder blithely mixes his tenses in Our Town!